The following program, written in C, writes data all

over the data section, starting from the local variable i. Compile and

run the program, then answer the questions. Note that the results vary

with different compilers and operating systems, so specify the systems

you used.

Note the behavior of the while loop. The first statement in the loop

(*j=0;) writes a zero to the RAM address stored in variable j. The

second statement (j=j-1;) moves the address downward in RAM each

time the loop executes. Each step of j moves by a short integer,

which is 2 bytes (16 bits) long.

main() {

short i, *j;

j = &i;

while(1) {

*j = 0;

j = j-1;

}

}

(a) Describe what happens when the program runs.

(b)Does the program behave differently if we store a nonzero value in

the first statement in the while loop? For example, substitute 21845

(in hex, 0x5555, alternating 0s and 1s). Describe what happens.

Try another numerical value and describe what happens.

(c) Does the program behave differently if we add 1 instead of

subtracting 1 in the second statement? Try it while storing zeros

and find out. Describe what happens.

(d)Repeat part (c), but use a nonzero value as described in part (b).

(e) Write a program that reads text into an input buffer that is 10 bytes

long. Run the program and type in 20 bytes. What happens? Do you get a different result if you use a different language, for

example, C versus Java?

(f) Look up information about the Morris worm. Identify other

vulnerabilities that the worm used to propagate.